Process for the preparation of n1-alkanoylated sulfanilamidopyridazines



United States Patent Ofitice 3,fil,702 Patented Aug. 28, 1962 3,051,702 PROCESS FOR THE PREPARATION OF N -ALKA- NOYLATED SULFANELAMIDGPYRIDAZHNES Gilmer T. Fitchett, Greenbrook Township, and .lohn E. Gordon, Bridgewater Township, Somerset County, and Robert G. Shepherd, Ridgewood, NJ, assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine N0 Drawing. Filed lune 21, 19643, Ser. No. 37,576 3 Claims. (Cl. 260-2395) This invention relates to a process of preparing N acylsulfanilamido pyridazine and alkoxypyridazines.

Many sulfa drugs of the sulfanilamidopyridazine type have an objectionable bitter taste, which makes their oral administration unplesant and less satisfactory. For example, 3-sulfanilamido-6-methoxypyridazine exhibits an especially objectionable bitter taste. It is known that in general N -acyl derivatives, such as the N -formyl, N -acetyl and N -propionyl derivatives, do not have the objectionable, strongly bitter taste but do retain substantially the therapeutic activity of the parent drug.

In spite of the very real advantages in using the N acyl derivatives, they have not achieved the wide acceptance that their improved properties would seem to warrant. This is laregly due to the extreme diificulty encountered in preparing some of these compounds and which causes the production cost to be so high that their practical utilization has been seriously limited.

For production purposes, it is found that direct acylation of the parent sulfa drug is not practical. This is due to presence of the amino group. It, too, is readily acylated and therefore there is a tendency to form N ,N -diacylates.

In the case of the preparation of N -acyl-3-sulfanilamido-6-methyoxypyridazine, it has been proposed to overcome this by blocking off the N nitrogen by reaction with carbobenzoxy chloride. The N group is then acylated, and thereafter the carbobenzoxy group is removed, as by catalytic hydrogenation of other reduction procedures. Although this constituted an appreciable forward step in the preparation of N -acylsulfamethoxypyridazine, it still is not wholly satisfactory. The method is complicated, it requires a number of steps and there is a loss in yield. The net result is that production cost is still high enough to constitute a limitation on the field of use.

According to the present invention, an extremely simple process of preparing the desired N -acyl derivatives has been found. The desired result is obtained by reacting the N amino group with an aromatic aldehyde, such as benzaldehyde, tolualdehyde, anisaldehyde,veratraldehyde, and the like, to form an anil. The resultant N -aralkylidene compound is then acylated at the N position using acylation procedures which are quite simple. That which is preferred to use the corresponding anhydride, in the presence of a suitable antacid liquid heterocyclic tertiary amine base, such for example as pyridine, picoline and the like. After acylation is completed, removal of the aralkylidene group can be effected simply by adding some water to the reacted mixture and gently heating, whereby the aralkylidene groups is hydrolyzed off and the N amino group is regenerated. Thereafter, addition of further water causes a precipitation of the desired N -acyl product which can be recovered readily as by conventional filtration.

Differential hydrolysis of the aralkylidene group therefore constitutes a principal feature of the present invention. That this can be accomplished is highly surprising. The reasons for the almost complete selectivity are not known. It is not desired to limit the invention to any particular theory or reaction mechanism. That it would be possible under sufficiently drastic conditions to hydrolyze off the aralkylidene group is, of course, known to every chemist. However, there are precisely the type of reaction conditions which are also known to effect hydrolysis of an acyl group on an N nitrogen. The surprising thing is that the very conditions which normally effect hydrolysis of both types of groups in the present cases hydrolyze only the one without any substantial hydrolysis of the other.

The new process permits formation of pure N -acyl sulfa drugs in good yield in a simple process in which most of the steps are effected without isolating any material from the reaction mixture. Thus, it is possible for the first time to produce N -acyl sulfa drugs such as N acyl sulfamethoxypyridazine at a cost only slightly above that of the sulfa drug itself. A wide field of use is thus assured since at slight additional cost the improved products, with no bitter taste, are obtainable.

Some of the N -aralkylidene compounds are new chemical compounds and are claimed as such since they constitute intermediates useful in the present process for the production of the N -acyl products. When it is desired to isolate the aralkylidene compounds, this may be effected easily from the aqueous reaction medium by precipitation with various organic liquids, such as ether.

Further advantages of the invention are that the various steps do not require elaborate equipment or procedure. For example, the formulation of the anil by reaction of the aromatic aldehyde with the original sulfa drugs proceeds simply and easily in an alcoholic medium. Isolation of the anil is also simple and the acylation is effected at very moderate temperature, for example 45 C. with good yield. The temperature of hydrolysis is also very moderate, about 40 C., although in no sense critical, and the isolation with further additions of water takes place simply and easily, producing a very pure product in excellent yield.

Acylation can be eifected over a very wide range of tem-.

peratures, from about minus 15 C. to 60 C. Since reaction at the lower temperatures is quite slow and the yield is substantially as good at about 40 C., temperatures in this general range are preferred.

The amount of the lower aliphatic acid anhydride used also is not critical. It may range from stoichiometrical amounts to as much as a 10 parts per part of N -aralkylidene sulfa drug. There is some advantage in operating slightly above the absolute minimum, as easier control of the reaction results. In general, a range of from 0.6 part of anhydride per part of aralkylidene to equal parts constitutes a desirable practical operating range.

The amount of antacid, for which as is pointed out above, the liquid heterocyclic bases are suitable, is also not critical. In general, it ranges from 2 parts to parts. Here again, there is some advantage in operating slightly above the minimum and so for practical operation a range of from about 3.5 to 6 parts gives excellent 01)- rating conditions and does not result in excessive cost.

The amount of water which has to be added to the acylation mixture is likewise not critical. Minimum amounts less than & part per part are not fully efiective and the hydrolysis will proceed satisfactorily even with as much as 10 parts of water. The hydrolysis temperature can vary from 0 to C., but may be advantageously in the 40s to obtain rapid reaction with simple control. Final precipitation can be effected with the addition of from 2 to 50 parts of water, but for practical operating procedures, 1 or 2 parts of water for the hydrolysis and from 10 to 15 parts of water for precipitation give excellent results.

The invention will be further illustrated in the following specific examples in which the parts are by weight, unless otherwise specified.

Example I 70 parts of a mixture of 3-sulr'anilamido-6-methoxypyridazine and 550 parts of anhydrous ethanol was heated to reflux. To the slurry was then slowly added 50 parts of benzaldehyde. Within a short time, a few minutes, a complete solution resulted and the temperature was maintained at 70-78 with agitation until the reaction was complete. In a few minutes the product started to crystallize. The slurry was cooled to about 20 C. and a solid product was removed by filtration and washed with anhydrous ethanol and dried. A high yield of N -benzylidene-3.-sulf ani1amido-6-methoxypyridazine resulted.

Example 2 A mixture of 980 parts of pyridine and 162 parts of acetic .anhydride was heated to 40 C. 250 parts of the product of Example 1 was then added, the temperature being maintained between 40 and 45 C. After the addition was completed, agitation was continued until reaction was complete. Precipitation of solid material started early and after cooling the mixture to 25 C., 250 parts of water was added. The temperature of the slurry rose to 46 C. and complete solution resulted in a short time. The solution was maintained at 40 C. until hydrolysis of the benzylidene group was complete and it was then cooled to 30 C. 2100 parts of water was then added, which precipitated the product after cooling to 20 and short agitation. The solid product was removed by filtration, washed pyridine free and dried, giving a good yield of N -acetyl-N -(6-methoxy-3-pyridazinyl)- sulfanilarnide.

Example 3 The procedure of Example '1 was repeated except that the benzaldehyde was replaced by an equivalent amount of anfisaldehyde. An. excellent yield of N -anisylidene sulfamethoxypyridazine was obtained.

Example 4 sulfamethoxypyridazine was added. The mixture was stirred at 45 C. and complete solution occurred. In

5-10 minutes, a precipitate formed and the heating at 5 45 was continued for 1 hour. The slurry was cooled to 15 C. and 850 parts of diethyl ether was added to the slurry. The slurry was cooled to C., the crystals isolated by filtration and dried to constant weight and a 90.5% yield of the expected product was obtained. The

melting point was 201.5202.9 C. and the microanalyti cal results agreed 'very well with the values calculated for N -acetyl-N-benzylidene sulfamethoxy pyridaz'ine.

Example 6 To 60 parts of pyridine was added 12 parts of 5 the mixture was agitated for .1 hour.

This application is a continuation-in-part of our co- .pending application Serial No. 712,682, filed February 3, 1958, now US. Patent 2,974,137.

We claim:

1. In a process for producing an N -acylated sulfanil- 15 amidopyridazine from an N -aralkylidene compound hav ing the formula ArOH=NSOrN wherein Ar is selected from the group consisting of phenyl,

tolyl, anisyl and veratryl, Py is selected from the group cohsisting of pyridazinyl, methoxypyridazinyl and dimethoxypyridazinyl and Ac is selected from the group consisting of formyl, acetyl and propionyl, the improvement which comprises: at a hydrolysis temperature in the range of from about 0 to about60 C., forming a reaction mixture comprising 100 parts of said N -aralkylidene compound, from about 10 to about 1000 parts of water, from about 200 to about 5000 parts of a liquid amine base selected from the group consisting of pyridine and picoline and from about the stoichiometrically equivalent amount to about ;l,000 parts of a lower alkanoic acid, whereby dissolution of said N -aralkylidene compound and selective hydrolysis of the N substituent is initiated; maintaining said mixture at a temperature within said hy drolysis temperature range until hydrolysis is substantially complete and isolating the resultant N -acylated product.

2. A process according to claim 1 in which said isolation of said product comprises adding from about 200 to about 5000 additional parts of water, whereby said hydrolyzed reaction product is precipitated, and collecting resultant precipitate.

3. A process according to claim 1 in which Ar, is phenyl, Py is 6-rnethoxypyridazinyl and Ac is acetyl.

0 References Cited in the file of this patent UNITED STATES PATENTS 2,429,835 Martin et a1 Oct. 28, 1942 2,833,761 Murphy et a1 May 6, 1958 5 FOREIGN PATENTS 560,661 Great Britain Apr. 14, 1944 OTHER REFERENCES Kollofi et al.: Journal American Chemical Society,

vol. 62, pages 158-160 1940 

1. IN A PROCESS FOR PRODUCING AN (1- ACYLATED SULFANILAMIDOPYRIDAZANE FROM AN N4-ARALKYLIDENE COMPOUND HAVING THE FORMULA 